Precision Soil Sampling Strategies for Agricultural Fields of West Tennessee
Grant, T., H. J. Savoy, and B. G. Leib.  2014.  ASA, CSSA & SSSA International Annual Meeting, Long Beach, CA November 2-5, 2014.

Abstract:
Timothy Grant1, Hubert J. Savoy Jr.2 and Brian Leib2, (1)Biosystems Engineering and Soil Science, University of Tennessee, Knoxville, TN (2)University of Tennessee - Knoxville, Knoxville, TN Precision soil sampling is a crucial step in implementing a site-specific nutrient management plan. Agricultural fields exhibit minimal to very high degrees of spatial nutrient variability. Blanket applications of nutrients can be environmentally harmful and economically wasteful. Most fields will have areas under-fertilized, limiting yield potential, as well as areas over-fertilized, potentially losing applied nutrients to the environment. Precision soil sampling looks to minimize improper fertilization by better characterizing spatial variability than a single composite field value. Grid sampling and management zone sampling are used in precision sampling, differing in time and labor required, and prior knowledge necessary. This research looks to evaluate precision soil sampling methods, zone delineation techniques, and numbers of subsamples required to achieve consistent analysis results in west Tennessee agricultural fields. Two fields were sampled in Milan, TN, one being highly variable in soils, landscape, and yield potential and the other displaying little variation. Fields were divided into one-acre grids and sampled at each grid center and randomly throughout each grid. Grid center samples will be grouped by zones based on soil and yield maps. A two-acre section of each field was divided into nine grid squares and sampled intensively, then sampled in triplicate at five levels of subsample intensity as a whole. Macronutrients phosphorus and potassium exhibited higher variation across both fields in grid center samples than in grid cell samples, while pH, magnesium and calcium either showed similar or higher variation in grid center samples across both fields. Readily available Web Soil Survey maps, intensely surveyed soil maps, and cotton yield maps all grouped variation compared to whole field variation.